Process for preparing tetravinyl lead



United States Patent 3,156,716 PRQCESS FGR PREPARl-NG TETRAVINYL LEADHugh ll. Ramsden and Hugh F. Shannen, Scotch Plains,

N..l., assiguors to Esso Research and Engineering (Compauy, acorporation of Delaware No Drawing. Filed .Tan. 24, 1963, Ser. No.253,742 7 Claims. (Cl. 260-437) The present invention is concerned withthe preparation of organolead compounds. In particular, it is concernedwith an improved process for the preparation of tetravinyl lead.

It is known in the art that olefinic lead compounds, either alone or incombination with other suitable lead alkyl anti-knock additives in motorfuel, are elfective antiknock agents. These lead olefinic anti-knockadditives include those organo-lead compounds that possess one or moreolefinic groups wherein the said olefinic groups are attached directlyto the lead atom and comprise from 2 to 8 carbon atoms in each group or8 to 32 carbon atoms in total. In particular, those olefinic leadcompounds having olefinic radicals comprising one or more vinyl groups,such as tetra-allyl lead, tetracrotyl lead, tetrapropenyl lead,tetramethylallyl lead, mixed lead alkenyls such as divinyl diallyl lead,vinyl allyl dicrotyl lead and vinyl allyl crotyl methylallyl lead andother suit able combinations of the foregoing olefinic compounds aredesirable additives for motor fuels.

A preferred anti-knock agent from the above class of compounds has beenfound to be tetravinyl lead. Use of minor amounts of tetravinyl lead ingasoline gives very effective anti-knock activity. In fact, it has beendiscovered that tetravinyl lead is superior in anti-knock ability to thelead alkyl compounds, in particular tetraethyl lead, at the sameadditive levels. Therefore, a process adaptable to the commercialproduction of tetravinyl lead is of great interest and extremeimportance to the members of the automotive and petroleum industries.

Tetravinyl lead is a relatively new compound which has been recentlysynthesized. Two methods for the preparation of tetravinyl lead aredescribed in the article in Angewandte Chemie, volume 71, page 161(February 21, 1959), entitled Preparation of Tetravinyl Lead, by LudwigMaier. These methods, as disclosed by the aforementioned reference, canbe summarized by the following two reactions:

(2) PbCl -I- 4CH =CHMgBr Pb (CH:

While both methods do produce the desired tetravinyl lead product, theyields are so poor as to make the proccases of little value outside ofproducing small laboratory size amounts of the compound. Typical yieldsreported by Maier are 17.2% of theory for method (1) and 9.1% by method(2).

A contemporary article of Maiers described a procedure which wasanalogous to method (2).

The article. entitled Preparation of Tetravinyllead and Some Phenyl-3,156,716 Patented Nov. 10, 1964 method (1) since ammonium chloride is aproduct of that method and therefore the deficiency of yield isseemingly inherent in the reaction itself. The method using leadchloride (PbCI as practiced by Juenge and Cook, proved to be anextremely difficult reaction to control. During the addition of solidlead chloride to the vinyl Grignard solution, heat surges occurredaccompanied by the generation of great volumes of gas. The reaction wascarried out at high temperatures with an excess of the Grignard in orderto prevent the formation of hexavinyldilead. This compound can beconverted to tetravinyl lead only by repeated and hazardousredistillations; hazardous because of the likelihood of explosivedecompositions.

The conditions employed in the above .preparation result in a largeamount of decomposition as evidenced by the large amounts of gasevolved. It is further evidenced by the great amounts of solid,presumably polymers, obtained by Juenge and Cook during their work-up.Thus it is not so surprising that the over-all yield was so poor.Special care was required during the work-up and purification of thereaction product since the tetravinyl lead so obtained decomposedexplosively when heated over C. Furthermore the product prepared by thisprocedure was found to be unstable at room temperature and requiredcareful storage at very low temperatures in the absence of light.Over-all this procedure could not be considered suitable for large scalepreparations due to the combined factors of poor yield, hazardouswork-upconditions and the instability of the product obtained.

It has now been found that tetravinyl'lead can be prepared from leadchloride and vinyl .Grignard by an improved process whereby high yields,safe work-up and a stable product are obtained. This process is easilycontrolled and eliminates the heat surges previously associated withthis synthesis. Decomposition during the reaction is minimal so thatlittle or no gas evolution is found. This also results in a very greatreduction in the amount of polymer produced. The relative absence ofpolymer aids in simplifying both the solvent stripping and productdistillation steps.

The product obtained from this improved process is of very high purity(about 99%) as determined by lead analysis. Unlike the material preparedby the previous ly known processes, the tetravinyl lead of the presentprocess has been found to be stable on storage at room temperature indark bottles. Samples stored under those conditions for as long as sixmonths did not show any sign of decomposition.

This improved process consists of adding a solution of vinyl Grignard,previously prepared by methods well known in the art, i.e. by reacting avinyl halide, e.g. vinyl chloride, with magnesium, to a slurry of leadchloride in a suitable inert solvent. Suitable inert solvents for thepreparation of the vinyl Grignard and for use in the lead chlorideslurry include te'trahydrofura'n, diglyme and related diethers ofethylene and polyethylene glycols, e.g. ethylene glycol dimethyl ether.An especially preferred inert solvent is tetrahydrofuran. The solventused in preparing the Grignard and that used in the lead chloride slurrymay be the same, difierent, or each may be mixtures of the above type ofsolvents.

Furthermore, it has been found that inert liquid hydrocarbons may beadded to the reaction mixture to thin the slurry thereby allowingefiicient mixing. Suitable inert liquid hydrocarbons include normal andiso alkanes, cycloalkanes, aromatics, alkyl substituted aromatics, etc;It is preferred that the hydrocarbon boil below about roe- C. in orderto allow the stripping of the solvent to be accomplished withoutexcessive heating. Preferred liquid hydrocarbons include n-pentane,benzene and cy- Gt clohexane. A most preferred liquid hydrocarbon isn-pentane. The addition of the hydrocarbon diluent may be made beforethe Grignard solution is added or during the course of the Grignardaddition. The temperature (during the addition of the major part of theGrignard solution) is kept below 40 C. After the addition is completed,the mixture is heated at reflux for several hours, e.g. 1-6 hours,preferably 2-4 hours. After cooling and filtration, the filtrate isstripped of all solvents. The concentrated mixture is then distilledunder vacuum to yield the desired tetravinyl lead, which is collected inthe temperature range of about 24-35 C. at l-3 mm. pressure. During thisdistillation the pot temperature is maintained below 75 C. By keepingthe lead chloride concentration in great excess during the addition andby careful temperature control, yields of 80% and greater are readilyobtainable.

The process will be more completely understood from a consideration ofthe following examples. It is understood that these examples areadvanced for the purpose of illustration and should not be construed aslimiting the scope of the invention in any manner.

Example I A solution of 5.0 moles of vinylmagnesium chloride (preparedby reacting 5.5 moles of vinyl chloride and 5 gram atoms of magnesium)in 1200 ml. of tetrahydrofuran was added dropwise to a stirredsuspension of 667.4 grams of lead chloride in 1000 ml. oftetrahydrofuran. After about one-quarter of the Grignard solution hadbeen added, the suspension, which had been black from the firstaddition, became thick. At this point 1000 ml. of pentane was added tobreak up the slurry. The Grignard solution was completely added in about4 hours and during the major part of this time the temperature wasmaintained below 40 C. Near the end of the addition the temperature wasallowed to rise until it reached a final value of about 46 C. Thereaction mixture was then heated to reflux and maintained at thattemperature (49 C.) for about 2 hours. It was then allowed to standovernight during which time a black precipitate settled out. Thisprecipitate was filtered off and the filtrate was stripped of solventunder reduced pressure. The residue, including some precipitated saltsand polymer, was then vacuum distilled. Tetravinyl lead was obtained inthe fraction distilling from 24 C. to 34 C. at 1-3 mm. (absolute).During this distillation, the pot was heated by means of a water bathand the pot temperature was not allowed to exceed 65-75 C. The bathtemperature at final dry point was 80 C. Tetravinyl lead was obtained ina yield of 298.4 grams or 79%. However, additional amounts of productwere found to be present in both the residual salt cake and thedistillation fore runs so by recycling these materials, even higherprocess yields can be obtained.

Example II The process of Example I was scaled up by a factor of 20times (29-30 pounds of lead chloride) and run in pilot plant equipmentwithout any noticeable difiiculty. It is therefore evident that thisprocess can be used safely in the large scale preparation of tetravinyllead.

Example III The process of Example I wherein ethylene glycol dimethylether is used as solvent yields tetravinyl lead in high yield.

Example IV The process of Example I wherein benzene is added as thehydrocarbon diluent yields tetravinyl lead in high yield.

Example V The process of Example I wherein cyclohexane is added as thehydrocarbon diluent yields tetravinyl lead in high yield.

Example VI The process of Example I wherein the vinyl Grignard isprepared from vinyl bromide and magnesium yields tetravinyl lead in highyield.

What is claimed is:

1. An improved process for the preparation of tetravinyl lead comprising(1) slowly adding a vinyl Grignard solution to a slurry of lead chlorideeach in an organic ethereal solvent at a temperature maintained belowabout 40 C. during the major part of said addition the amount of saidorganic ethereal solvent being sufiicient to allow efiicient mixing ofsaid slurry, (2) refluxing the mixture and (3) distilling under reducedpressure while maintaining the pot temperature below about C. to recoversaid tetravinyl lead as a distillate fraction.

2. An improved process for the preparation of tetravinyl lead comprising(1) slowly adding a solution of vinyl magnesium chloride to a slurry oflead chloride each in an organic ethereal solvent at a temperaturemaintained below about 40 C. during the major part of said addition, (2)adding a slurry thinning amount sufficient to allow efficient mixing ofsaid slurry of an inert hydrocarbon diluent, (3) refluxing the mixtureand (4) distilling under reduced pressure while maintaining the pottemperature below about 75 C. to recover said tetravinyi lead as adistillate fraction.

3. The process of claim 2 wherein the inert solvent of step (1) istetrahydrofuran.

4. The process of claim 2 wherein the inert hydrocarbon diluent of step(2) is n-pentane.

5. An improved process for the preparation of tetravinyl lead comprising(1) slowly adding a solution of vinylmagnesium chloride intetrahydrofuran to a slurry of lead chloride in tetrahydrofuran at atemperature maintained below about 40 C. during the major part of saidaddition, (2) adding a slurry "thinning amount sufficient to allowefiicient mixing of said slurry of n-pentane, (3) refluxing the mixtureand (4) distilling under reduced pressure while maintaining the pottemperature below about 75 C. to recover said tetravinyl lead as adistillate fraction.

6. The process of claim 5 wherein the refluxed mixture of step 3 isallowed to stand at a lower temperature until a precipitate settles out,is filtered free from said precipitate and is stripped of solvent priorto the distillation of step 4.

7. An improved process for the preparation of tetravinyl lead comprising(1) slowly adding a solution of vinylmagnesium chloride in an inertorganic ethereal solvent selected from the class consisting oftetrahydrofuran, the di-ethers of ethylene glycols and the di-ethers ofpolyethylene glycols to a slurry of lead chloride in an organic etherealsolvent selected from said class at a temperature maintained below about40 C. during the major part of said addition; (2) adding a slurrythinning amount sufficient to allow efiicient mixing of said slurry ofan inert hydrocarbon solvent boiling below about C.; (3) refluxing theresulting mixture; (4) cooling said mixture until a precipitate settlesout; (5) filtering off said precipitate to yield a solids free filtrate;(6) stripping off said inert solvent from said filtrate and (7)distilling the residuum of step (6) under reduced pressure whilemaintaining the pot temperature below about 75 C. to recover saidtetravinyl lead as a distillate fraction.

References Cited in the file of this patent UNITED STATES PATENTS3,071,607 Juenge Jan. 1, 1963

1. AN IMPROVED PROCESS FOR THE PREPARATION OF TETRAVINYL LEAD COMPRISING(1) SLOWLY ADDING A VINLY GRIGNARD SOLUTION TO A SLURRY OF LEAD CHLORIDEEACH IN AN ORGANIC ETHEREAL SOLVENT AT A TEMPERATURE MAINTAINED BELOWABOUT 40*C. DURING THE MAJOR PART OF SAID ADDITION THE AMOUNT OF SAIDORGANIC ETHEREAL SOLVENT BEING SUFFICIENT TO ALLOW EFFICIENT MIXING OFSAID SLURRY, (2) REFLUXING THE MIXTURE AND (3) DISTILLING UNDER REDUCEDPRESSURE WHILE MAINTAINING THE POT TEMPERATURE BELOW ABOUT 75*C. TORECOVER SAID TETRAVINYL LEAD AS A DISTILLATE FRACTION.